Plate & bar impact experiments were performed on glass to investigate the mechanisms responsible for recently observed failure waves. Observations are reported showing that the so-called failure wave is actually a propagating boundary of damaged material. It inititates at the specimen surface, without appreciable incubation time, & propagates to its interior. In-material gauge measurements show that the spall strength & shear resistance are drastically reduced behind the failure wave front. Shear resistance interferometrically measured in pressure-shear experiments is in agreement with the in-material gauge records. Normal stress measurements performed close to the impact surface show a progressive reduction in normal stress behind the failure wave.
